1. Field of the Invention
The invention relates to an assembly method of a rotary shaft in use for a ball-bearing type turbocharger which is intended to leave out complicating procedures necessary when carrying out imbalance-correction of a turbine impeller to readily facilitate the imbalance-correction, and contribute to an improved production with an extended period of service life.
2. Description of Prior Art
In a ball-bearing type turbocharger there is a rotary shaft rotatably supported by first and second ball bearings. To one end of the rotary shaft, a turbine impeller is securely connected through its boss portion, and to the other end of the rotary shaft, a compressor impeller is connected by a nut securing the compressor impeller against its removal.
Prior to disposing the rotary shaft into the ball-bearing type turbocharger, an inner race of the first ball bearing is forcibly inserted to the rotary shaft by press-fit until one side of the inner race engages with the boss portion of the turbine impeller. Subsequent to the press-fitting procedure, an imbalance-correction of the turbine impeller is carried out with the inner race of the first ball bearing inserted to the rotary shaft.
After press-fitting the inner race of the first ball bearing, however, it becomes difficult to insure a tight engagement between an entire surface of one side of the inner race and that of the boss portion of the turbine impeller due to spring-back of the inner race, although one side of the inner race temporarily engages with the boss portion of the turbine impeller at the time of press-fitting the inner race of the first ball bearing. This makes it impossible to maintain a perpendicular relationship between a center line of the rotary shaft and a ball-rolling plane of the inner race of the first ball bearing. Then, an amount of imbalance of the turbine impeller is measured in an futile attempt to carry out the imbalance-correction with a center line of the inner race out of place from that of the rotary shaft.
At the time when the rotary shaft is disposed within the turbocharger, the inner race normally moves to an intended position in which the inner race engages its one side with the boss portion of the turbine impeller so as to accumulate the amount of imbalance of the turbine impeller too much to correct once the rotary shaft is disposed in the turbocharger.
Therefore, it is an object of this invention to provide an assembly method of a rotary shaft in use for a ball-bearing type turbocharger which is capable of facilitating to carry out imbalance-correction of a turbine impeller, and contributing to an improved production with an extended period of service life.